In recent years, there have been developed an eyeglass type wearable display (hereinafter referred to as WD) and a headcount type display (hereinafter referred to as HMD) for the purposes of improvement of workability by a hand free way, information retrieval, vision correction for weak-sighted persons and practical experiences of various types of amusements.
A lens of WD or of HMD is provided with an optical substrate that guides an image coming from a display unit to the eyes optically. This optical substrate is provided with a hologram element which represents a reflection layer that reflects an image displayed by a controller of WD or of HMD on LCD or on an organic EL display.
For mounting the hologram element on the optical substrate, there is generally employed a method wherein a hologram element which has been subjected to laser exposure at a predetermined position on a thin-film-shaped unexposed hologram photosensitive sheet (hereinafter referred to as a hologram photosensitive sheet) is cut to be in predetermined form and size corresponding to the shape of an inclined surface representing a reflection surface of the optical substrate, to be stuck on a predetermined position on the optical substrate as a thin-film-shaped hologram element.
In each of WD and HMD on which a hologram element is provided in the aforesaid way, the weight is lighter, the power consumption is less and the life span is longer, compared with one employing no hologram element. It is further possible to realize a see-through type wherein a prism is used not to block the field of vision, and a real image of the actual scene and a virtual image of the hologram image can be seen simultaneously.
There has been suggested the following method as a method to stick a hologram element on a large-sized glass plate or the like effectively. Namely, an island-shaped hologram element and a positioning hologram element for positioning the island-shaped hologram element in the post-process are formed on the photosensitive sheet first by giving exposure to the hologram photosensitive sheet by the use of a mask on which a hole of the island-shaped hologram element forming portion and a positioning hole are provided. Next, this photosensitive sheet is interposed between a pair of protective sheets through adhesive layers to form laminated sheets. Further, slits are made on the aforesaid island-shaped hologram element portion and on a contour or a circumference of the positioning hologram element, from the protective layer on one side of the laminated sheet. By taking up the protective sheet on one side among the laminated sheets and a photosensitive sheet by a roller provided on a conveyance path through which the laminate sheet on which the slits are made is conveyed, an area other than the area on which the slits are made among the protective layer on one side and the photosensitive sheet, namely, an area portion other than a portion for the island-shaped hologram element and positioning hologram element, is separated from the protective sheet on the other side, and it is separated from the conveyance path. After that, a portion that is stuck on the island-shaped hologram element and on the positioning hologram element to stay without being separated among protective sheets on one side, namely, a portion on which slits are made on protective sheets on one side is stuck on one side of two-sided gluing agents to be removed. At this stage, there turns out to be the state wherein an island-shaped hologram element portion and a positioning element portion are stuck on the protective sheet on the other side to stay. Further, by detecting the positioning hologram element portion with a detecting mechanism, the island-shaped hologram element portion is positioned to be stuck, and at its position, the protective sheet on the other side and the adhered island-shaped hologram element portion are stabilized, then, the island-shaped hologram element portion is pressed by the roller against an object for adhesion from the upper part of the protective sheet on the other side to be stuck, and the protective sheet on the other side is taken up by the roller after the adhesion force is further enhanced, to be peeled off the island-shaped hologram element portion. Thus, the island-shaped hologram element portion only is stuck on an object for adhesion in the aforesaid way (Patent Document 1).
However, on WD and HMD, an inclined surface of an optical substrate on which a hologram element is stuck is small, and accuracy for laser exposure that is higher than that in the ordinary hologram element forming is required. Therefore, it is difficult to form accurately interference fringes through laser exposure at the predetermined position on a hologram photosensitive sheet that serves as an optical element of WD and HMD, which is a problem. Further, even if the hologram element of higher accuracy is formed, there still is a problem that it is difficult to specify the predetermined position for the laser exposure and to cut the hologram element to be in a predetermined form to stick the hologram element in the predetermined form on a small inclined surface of optical substrate accurately. There is further a problem that distortion and discoloration are observed on images when images are guided to eyes by wearing a completed WD or HMD, if the hologram element on which interference fringes are formed accurately is not stuck on the predetermined inclined surface of optical substrate. This causes a problem that the production efficiency of highly accurate optical substrate (hereinafter referred to as hologram optical substrate) on which a hologram element is stuck is lowered and production cost is increased.    Patent Document 1: Japanese Patent Publication Open to Public Inspection No. 10-109811